Intraocular pressure (IOP) is an extremely important characteristic of a physical state of the eye, especially in glaucoma patients and therefore needs periodic, and sometimes permanent monitoring.
The IOP measuring technique most widespread at present is the application of a static pressure to the corneal surface and determination of IOP against its deformation parameters, diameter of the applanation circle, or the depth of deformation for estimation of IOP.
However, such a method requires, on the one hand, preliminary anesthesia application, and on the other hand it provides for a direct contact of the force-transmitting element with the corneal surface, which involves obligatory subsequent sterilization, since the aqueous humor of the eye is in fact an infection transmitter. Use of disposable intermediate elements, however, does not make anesthesia no longer necessary.
Such a method is embodied in a device, comprising a transparent prism, a reference circumference being provided on the prism working surface, having a diameter corresponding to a normal IOP. The device however, suffers from all the disadvantages inherent in the method discussed above.
These disadvantages have been overcome in a device according to French Pat. No. 2,542,603, which provides for IOP measurement through the patient's eyelid. Said device comprises a solenoid with a movable armature, said solenoid being enclosed in a casing, a means for preliminary loading of the armature with a preset force, and a sensing element appearing as a piezosensor responsive to armature movement on its interaction with the cornea through the eyelid. Said sensing element is connected to a data processing unit. The device features rather sophisticated construction and its use for self-monitoring is impeded. Moreover, such a device needs periodic readjustment and recalibration, which is due to ageing of the sensing element. And finally, preliminary static loading of the patient's eye envisaged in the hydrostatic condition of the eye and introduces non-linear error into the measurement results.